Tokachi Plain Research Articles

Luminescence dating of sand matrices within gravelly fluvial deposits: Assessing the plausibility of beta dose rate calculation

Dating of gravelly fluvial deposits is typically hampered by the absence of suitable plant fragments for radiocarbon dating or sand layers for luminescence dating. Although gravelly fluvial deposits generally contain sand-sized quartz and feldspar that could be used for luminescence dating, the considerable grain-to-grain variability in beta dose rate, coupled with the lack of methods for routine dose rate estimation, presents challenges. In this study, a recently proposed model for calculating average beta dose rates in granular matrices was modified to be applicable to sand-sized dosimeter grains within gravelly deposits. We applied the modified model to sand-sized K-rich feldspars within sand matrices obtained from gravelly fluvial deposits in the Tokachi Plain, northern Japan, and compared the ages of samples obtained from sand matrices with those from sand lenses. Although the weight of <2 mm grains accounted for only 20%–35% of the bulk sediment, these grains were estimated to contribute approximately 70% of the external beta dose rate according to the model, because larger grains have a larger self-dose. Taking into account that the beta dose to dosimeter grains is mainly derived from smaller matrices (e.g. <2 mm), beta dose rates were also calculated based on the infinite matrix dose rate of the <2 mm fraction, along with the conventional water correction method. The ages of sand matrices calculated based on the beta dose rates derived from both the model and the infinite matrix dose rate of the <2 mm fraction were generally consistent with those of sand lenses. The dose rate calculated based on the model might be more accurate than that calculated using the infinite matrix dose rate of <2 mm fraction, but calculating the beta dose rate using the infinite matrix dose rate of <2 mm fraction is useful as a simple approach.

IRSL and post-IR IRSL dating of multi-grains, single grains, and cobble surfaces to constrain fluvial responses to climate changes during the last glacial period in the Tokachi Plain, northern Japan

Accurate chronologies of fluvial terraces are necessary to understand fluvial responses to climate and sea-level changes and uplift. Although feldspar post-infrared infrared stimulated luminescence (post-IR IRSL, or pIRIR) dating has been used to establish chronologies for Pleistocene fluvial terraces, the signals can be partially bleached in short, high-gradient river systems typical of Japanese rivers, resulting in overestimated ages. This study investigated aggradational fluvial terraces formed on the Tokachi Plain, northern Japan, during the last glacial period, and true depositional ages of the deposits were estimated by comparing multi-grain IRSL50/150, pIRIR50/150, and pIRIR50/225 ages, with single-grain pIRIR50/225 ages. IRSL50/225 and pIRIR50/225 ages of granite cobbles were also obtained and compared with the ages of multi-grains to evaluate the reliability of cobble ages. Fading-corrected IRSL 50/150 ages of multi-grains were consistent with pIRIR50/150 ages, indicating that the fading correction of IRSL50/150 signal was successful. Although equivalent dose distributions of single grains suggest that the pIRIR50/225 signal was completely bleached at deposition, pIRIR50/225 ages were slightly older than fading-corrected IRSL 50/150 and pIRIR50/150 ages possibly because of small residual doses. Fading-corrected IRSL50/225 and fading-corrected pIRIR50/225 ages of granite cobbles were consistent with the fading-corrected IRSL50/150 and pIRIR50/150 ages of multi-grains. However, comparison of cobble ages with climate records seems difficult due to their large errors. The fading-corrected IRSL50/150 and pIRIR50/150 ages of multi-grains indicate that fluvial aggradation occurred at 70–60 ka, followed by incision. Changes in the strength of East Asian summer monsoon precipitation are sufficient to explain fluvial evolution in the Tokachi Plain. Although some previous studies have argued that the ages of fluvial terraces might not be simply correlated to climate changes because of complex fluvial responses, significant changes in precipitation in the study area might have dominated the evolution of the entire fluvial system. Comparison with other fluvial systems in Japan suggests that slight differences in the responses of different fluvial systems to climate changes might be due to the spatial variability of those changes.

If Sakhalin spruce or Sakhalin fir die in windbreaks on seasonally frozen soils, what species can be recommended?

Soil of the Tokachi plain of eastern Hokkaido freezes during the winter due to low temperatures and light snowfall. Deciduous and fast-growing Japanese larch, Larix kaempferi, is often planted in arable land windbreaks to prevent wind damage to cultivation plants. Japanese larch is more resistant to winter desiccation than evergreen trees. However,windbreaks made of Japanese larch are disliked by many farmers because they shed a lot of branches and branchlets every year; if not completely removed from cultivation fields, branches and branchlets may damage agricultural tractors. Therefore, some farmers favor planting evergreen trees like Sakhalin spruce, Picea glehnii, or Sakhalin fir, Abies sachalinensis, both indigenous to Hokkaido. However, the disadvantage of these evergreen trees is that they are susceptible to winter desiccation. In settings where spruce and fir do not survive winter desiccation,planting of the evergreen Korean nut pine, Pinus koraiensis, is recommended. Although not native to Hokkaido, this species is less likely to suffer damage from winter desiccation than the other two evergreen species.

Arable land windbreak forests to reduce the impacts of fallen branches and branchlets from larch

In the Tokachi plain of eastern Hokkaido, Japanese larch, Larix kaempferi, is often planted in arable land windbreaks to prevent wind damage to sugar beets,potatoes, and beans during the spring cultivation season. Japanese larch is fast-growing and very effective in reducing wind damage in the early spring cultivation season, even if its buds are not open or its leaves are not fully extended. However, many farmers dislike Japanese larch arable land windbreaks because they shed a lot of branches and branchlets to cultivation fields every year, which may cause damage to agricultural tractors. Therefore, it is necessary to suggest a model of arable land windbreaks with less amount of fallen branches and branchlets of larches entering the cultivation field. It is recommended to plant three rows of trees: Japanese larch in the most windward and middle rows, and Japanese white birch, Betula platyphyllavar. japonica, in the most leeward row. Japanese larch in the most windward and middle rows reduces wind speed, whereas Japanese white birch in the most leeward row reduces branches and branchlets of Japanese larch entering cultivation fields.

Crop classification with multi-temporal and dual-polarimetric TerraSAR-X data

Crop maps are useful for agricultural field management and synthetic aperture radar data are attractive for generating crop classification because of their all-weather, all-day imaging capability. Additionally, classification algorithms are essential for generating accurate and multi-Grained Cascade Forest, which is also called ‘deep forest', was developed and its high performances have been shown for pattern recognition, voice recognition and so on. In this study, the capability of TerraSAR-X (including TanDEM-X) dual-polarimetric data for crop classification in the Tokachi Plain, Japan was investigated and the comparison of three different classification algorithms including classification and regression tree, random forests and deep forest was conducted.

Effectiveness of Japanese larch windbreaks during spring cultivation season: evaluation in local history chronicles, Tokachi plain

Effectiveness of Japanese larch windbreaks during spring cultivation season: evaluation in local history chronicles, Tokachi plain

十勝平野に分布するいわゆる"帯広火山砂"について

十勝平野に分布するいわゆる"帯広火山砂"について

広域地下水流動系を解明するための環境トレーサーと地下水位変動の有効性―十勝平野を例として―

広域地下水流動系を解明するための環境トレーサーと地下水位変動の有効性―十勝平野を例として―

Deposition pattern and sources of palynomorphs on the continental margin off Hokkaido Island, northwest Pacific

Abstract Hokkaido Island in northern Japan is located in a cool temperate to boreal climate zone influenced by summer monsoons and typhoons during summer–autumn, while its eastern area is influenced by the subarctic Oyashio Current. Palynomorph (pollen and spores) distribution was investigated in surface sediments from the shelf and slope (40–2300 m water depth) in the offshore area of Tokachi Plain, central-eastern Hokkaido Island. The objective of this study was to examine the source, transportation, and deposition of palynomorphs in marine environments. The majority of palynomorphs were transported from the Tokachi coastal plain by both strong local winds from the mountain areas during the spring–summer and the floods caused by heavy monsoon and typhoon rainfall. Approximately 10% of all palynomorphs were transported from both southwest and west areas by the wind. Palynomorph transportation by the Oyashio Current could not be discriminated because the same vegetation is present in Hokkaido and the islands in upper streams of the Oyashio Current. The total grain abundance was dependent on water depth. High concentrations were observed at depths of 700–1500 m, which is a region associated with high levels of fine silt and clay, suggesting that the transportation and deposition of palynomorphs are controlled by their grain sizes. This study supported a strong correlation between the distribution of sediments and the concentration of palynomorphs.

Time-lagged responses of indicator taxa to temporal landscape changes in agricultural landscapes

Biological indicator methods represent one of the most effective and widely used strategies for understanding the influences of environmental degradation on biodiversity in various landscapes. Researchers and land managers generally assume that the present distributions of biological indicator species are influenced by the current environment. However, recent studies have suggested the importance of past environments to species distributions (i.e., a time lag between changes in species distribution and habitat alterations). Therefore, it is necessary to understand the effects of past environments on the distributions of indicator species.We conducted a survey on the Tokachi Plain in Hokkaido, Japan. We targeted two taxa that have been widely used as indicator species (carabid beetles and bats) and investigated whether past landscape environments influenced their present distributions. We showed that past landscape environments (5 decades prior to the present) influenced the distributions of some ecological trait groups in each taxon (large body size for carabid beetles and a 25kHz peak echolocation frequency for bats) and that these effects varied among groups. Our results suggest the need to consider the dynamics of land-use changes and the effects of past environments on the distributions of indicator taxa, otherwise we may misunderstand the effects of environmental degradation on biodiversity.

北海道十勝平野におけるノスリの営巣パターンおよび営巣場所の特徴

北海道十勝平野において，ノスリButeo buteoの営巣パターンおよび営巣場所の特徴を調べた．調査期間中にノスリが営巣した場所は33ヶ所であった．ノスリは他の猛禽類の古巣にも営巣した．営巣木としてノスリにもっとも多く利用された樹種はカラマツLarix kaempferiであった．非営巣場所と比べて，営巣木は林縁からより離れた位置にあったが，それ以外の森林構造には営巣場所と非営巣場所違いはみられなかった．本研究の結果，ノスリの営巣場所の選好性は比較的弱く，このことが他種の古巣を利用した営巣や，カシワ林からカラマツ林へと主要な営巣環境をシフトすることを可能にしたと考えられた．その結果，十勝平野のノスリの営巣数は回復傾向にあるのかもしれない．

Analysis of Farmers&apos; Networks for the Dynamism of Large-scale Upland Farming in Tokachi Plain

Analysis of Farmers&apos; Networks for the Dynamism of Large-scale Upland Farming in Tokachi Plain

Edge‐related changes in tree communities in the understory of mesic temperate forest fragments of northern Japan

AbstractWe have assessed the effects of habitat fragmentation on understory tree communities in mesic temperate forests of the Tokachi plain of northern Japan. Tree community composition was analyzed across 13 forest fragments of various sizes ranging from 0.30 to 8.51 ha. The community composition varied along the edge‐to‐interior gradient: there was a lower abundance of shade‐tolerant shrubs in forest edges than in forest interiors, while saplings of dominant canopy trees and pioneer trees were more abundant near the edges. The edge influence extended approximately 56 m into the forest interiors. Even the interior area of small fragments were likely to be affected not only by the nearest edge but also by more distant edges. Consequently, most areas in fragments smaller than 2 ha were covered by these “edge‐type” communities. These results indicate that it is of primary importance to conserve and restore forests with an area at least larger than several hectares to sustain forest‐interior tree communities.

Consequences of forest fragmentation in an understory plant community: extensive range expansion of native dwarf bamboo

AbstractUnderstory bamboo species are important and influential components of temperate forests in at least several parts of the world. Here we report a study testing the effect of forest fragmentation on the dynamics of the dwarf bamboo Sasa chartacea and on forest herb communities in the Tokachi plain of Hokkaido, Japan. We studied 16 forest fragments of different sizes and small plots established in these fragments to examine the relationship between the abundance of S. chartacea, landscape and environmental conditions, and forest herb communities. Sasa chartacea was more abundant near forest edges and in smaller fragments, suggesting that the species has expanded its local range and increased its abundance in response to forest fragmentation. Edge‐related changes in light and soil moisture might have facilitated this range expansion. The species richness of forest herbs was strongly negatively related to the density of S. chartacea. Because much larger variation in species richness was explained by S. chartacea density than distance to the nearest forest edge, the expansion of S. chartacea has likely excluded other understory species by competition. In addition, the density of S. chartacea significantly explained variation in the species composition of forest herbs across plots. Taken together, our results emphasize the key roles of dwarf bamboos in changing plant communities following forest fragmentation.

Relative importance of the environmental factors at site and landscape scales for bats along the riparian zone

To conserve and manage the bat population in an agricultural landscape, we investigated the relative importance of environmental factors on their occurrence and abundance in riparian zones at site and landscape scales. From May to October 2003, four bat species (Myotis daubentonii, M. frater, Plecotus auritus, and Eptesicus nilssonii) were mist-netted at 26 sampling sites in five streams in the Tokachi plain in central Hokkaido, northern Japan. The environmental factors of the two scales were measured at each sampling site. To clarify the most suitable landscape scale for bats, we also compared three spatial extents (250, 500, and 750 m) at each site. Generalized linear mixed models revealed that the occurrence and/or abundance of all four species, except for M. frater, was positively correlated with the percent cover of broadleaved deciduous forest and the height of bank-side tree canopy. Additionally, according to variation partitioning, although the value of the pure effect varied among species and measurement types, the site scale had a relatively larger pure effect than the landscape scale in many cases. However, in three of the five combined models, the proportion of confounding effect was much larger than that of the pure effect at the respective scales. Our study demonstrated that streams adjacent to a well-developed broadleaved deciduous forest are important for night habitats of many bat species in an agricultural landscape. Although focusing on the site scale may be important for bat conservation, we strongly stress the necessity for conservation and management plans at multiple scales.

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

Many plant species currently exist in fragmented populations of different sizes, while they also experience unpredictable climatic fluctuation over time. However, we still understand little about how plant demography responds to such spatial and temporal environmental variability. We studied population dynamics of an understory perennial herb Trillium camschatcense in the Tokachi plain of Hokkaido, Japan, where a significant effect of forest fragmentation on seedling recruitment was previously reported. Four populations across a range of fragment sizes were studied for 6 years, and the data were analyzed using matrix population models. Per capita fecundity (the number of recruits per plant) varied greatly among populations, but the variation in population growth rates (lambda) was mainly driven by the variation in stasis and growth rates, suggesting that the general trend of reduced fecundity in fragmented populations may not be readily translated into subsequent dynamics. Temporal variation in lambda among years was more than 2 times larger than spatial variation among populations, and this result was likely attributable to the contrasting response of correlation structures among demographic rates. The among-population variation in lambda was dampened by negative covariation between matrix elements possibly due to density-dependent regulation as well as an inherent constraint that some elements are not independent, whereas positive covariation between matrix elements resulted in large temporal variation in lambda. Our results show that population dynamics responded differently to habitat fragmentation and temporal variability of the environment, emphasizing the need to discriminate these spatial and temporal variations in demographic models. Although no populations were projected to be declining in stochastic simulations, correlation between current habitat size and plant density implies historical lambda is positively related to habitat size.

Prediction of soil-freezing depth in Tokachi Plain under global warming condition

Prediction of soil-freezing depth in Tokachi Plain under global warming condition

Estimation of soil frost depth in Tokachi plain under global warming

Estimation of soil frost depth in Tokachi plain under global warming

Comparison of solid precipitation data by using 4 methods in Tokachi plain

Comparison of solid precipitation data by using 4 methods in Tokachi plain

P04 十勝平野に見られる前期〜中期更新世テフラの岩石学的特徴(ポスターセッション,日本火山学会2007年秋季大会)

P04 十勝平野に見られる前期〜中期更新世テフラの岩石学的特徴(ポスターセッション,日本火山学会2007年秋季大会)